Refrigeration apparatus



April 25, 1939. R. H. TULL. ET Al.

REFR IGERATION APPARATUS Filed sept. .3, 195e Illy ze l

lNvENToR ROBERT H. Tum.. No BAR-ral. d. Homxzs 'wmf ATToRN l PatentedApr. 25, 1939 UNITED STATES PATENT OFFICE REFRIGERATION APPARATUSaylvania Application September 3, 1936, Serial No. 99,180

5 Claims.

Our invention relates to refrigeration apparatus and particularly to atemperature and pressure control for the evaporator of a refrigeratingsystem.

In refrigeration apparatus for certain applications, for example,package sealing machines, wool shearing machines, and the like, it isnecessary to maintain a substantially constant temperature in anevaporator which has very little thermal storage capacity, and which issubject to sudden and appreciable changes in heat load. It is alsonecessary in many applications to prevent excessive moisture fromcollecting on the suction line from the evaporator which might drip andspoil the material which is being operated upon. Heretofore, the usualmethod of maintaining a substantially constant temperature was to cyclethe apparatus in response to heat load; in other words, the motordriving the refrigerator compressor was energized'when the evaporatorrequired refrigerationand was shut olf when the evaporator no longerrequired refrigeration.

However, such an arrangement required cycling controls, caused themachine to cycle too much as the load varied, and at intervals reducedthe suction pressure of the evaporator to such a low value that moisturecondensed on the suction line and dripped on the material operated upon.Furthermore, the success of this type of temperature control wasdependent on the evaporator having suflicient thermal capacity to storeup refrigeration to take care of the heat load for an appre- .ciableperiod of at least several minutes. The only way in which refrigerationcan be obtained from this type of evaporator, during the oil cycle, isto permit a rise in temperature, which in certain applications cannot bepermitted.

It is an object of our invention, therefore, to operate a refrigeratingmachine in such a manner that, if the amount of heat absorbed by theevaporator is varied or the capacity ofthe compressor is changedslightly due to variations in condensing pressure, the temperature ofthe evaporator will be maintained substantially constant, andfurthermore, to accomplish this resuit without the use of controls whichstop and start the motor in response to evaporator temperature.

It is another object of our invention to maintain a constant pressure inthe evaporator and in the suction conduit extending from the evaporatorso that the temperature of the evaporator and a portion of the suctionline remain substantially constant.

These and other objects are effected by our invention, as will beapparent from the following description and claims taken in connectionwith the accompanying drawing, forming a part of this application, inwhich:

y 'The single figure of the drawing illustrates diagrammatically arefrigerating system of the compression type embodying our invention.

Referring specifically to the drawing for a detailed description of ourinvention, numeral I designates a hermetically sealed casing whichencloses a motor 2 driving a compressori. Compressed refrigerant vaporis forced from the outlet of the compressor through a conduit 4 to acondenser 5, wherein the compressed refrigerant is liqueed due to thecooling action of air circulated over the condenser by a fan 6.Condensed refrigerant is conveyed through a conduit I to a liquidreceiver 8, the liquid receiver 8 and condenser 5 having suliicientcapacity to contain the entire refrigerant charge in the system.

Liquid refrigerant is conveyed from the receiver 8 to an evaporator IIthrough a conduit 9. 'I'he conduit 9 has a thermally responsiveexpansion valve I IJ interposed therein adjacent to the evaporator II.Refrigerant is vaporized in the evaporator II, and is conveyed, firstthrough a constant back-pressure valve, generally indicated at I2through a conduit I3, and from the backpressure valve I2, to theinterior of the sealed casing I through a vconduit I4. Refrigerant vaporis withdrawn fromv the interior of the sealed casing I through an inletI5 of the compressor 3, and the above-described cycle is then repeated.The motor 2 is energized from a line L1, la through conductors I6 andIl. A manually operated switch I8 isl provided for energizing the motor2 when refrigeration is desired,

The thermo-expansion valve III is provided with an inlet I8 and anoutlet I9, which outlet connects withthe evaporator II. The expansionvalve II) is also provided with a diaphragm 2|, a plungeractuated valve22 and an adjustable spring 23 which opposes the action of the diaphragm2I.

A bulb 24, filled with a suitable gas, is connectedl by a conduit 20 toa chamber 25 on the upper side of the diaphragm 2|.. Another conduit 26connects with a chamber 2l on the lower side of the diaphragm 2I andalso connects with terior of the evaporator II.

'Ihe thermo-expansion valve Il) is, therefore. responsive to both thepressure of the. evaporator II and the pressure of the gas in the. .bulb24 and conduit 20. Before the compressor 3 is started by closing theswitch I 8, the pressure in the evapothe inrator II is higher than thenormal operating pressure, due to the raising of the temperature of therefrigerant in the evaporator while the compressor has not been inoperation. Under this condition of abnormal evaporator pressure, theexpansion valve is closed because the high pressure refrigerant in theevaporator communicates with the underside of the diaphragm 2I throughthe conduit 26 and tends to raise the valve 22.

In accordance with our invention, refrigerant liquid is supplied to theevaporator I I in varying quantities, depending on the heat load, aslong as the motor and compressor are in operation, but thesuction-pressure and consequently the temperature of the evaporator andthe portion of the suction line between the evaporator and the backpressure valve are maintained substantially constant. In order to effectbalance of heat load and condensing unit capacity without starting andstopping the motor 2 in response to the pressure or temperature of theevaporator, a constant pressure valve I2 is inserted in the conduitbetween the evaporator and the compressor. The constant pressure valveI2 is provided with a diaphragm 28 and a plunger valve 29. A spring 3lopposes the pressure acting on the diaphragm 28 through the conduit I3.The plunger valve 29 operates to adjust the ow of refrigerant through anorifice 32 which is provided between the conduit I3 and a chamber 33communicating with the suction conduit I4.

As soon as the compressor 3 is started, there is an immediate reductionin pressure in the vevaporator II, which reduction of pressure istranslated to the chamber 21 on the under side of the diaphragm 2I ofthe expansion valve ill, thus tending to force the valve plunger 22downwardly and permit refrigerant to flow from the conduit I8 through anorifice 34 in the expansion valve IIS and out through conduit I9 to theevaporator Ii, which refrigerant boils at a temperature corresponding tothe pressure in the evaporator. The gas in the bulb 24 being warm due tothe inactivity of the compressor, exerts pressure through the conduit 20on the upper surface of the diaphragm 2l and also tends to hold theexpansion valve open and flood the evaporator II with refrigerant. Morerefrigerant is thus admitted to the evaporator than can be vaporiaed andsome of the refrigerant reaches the suction conduit I3 producing acooling ehect on the gas in the bulb 24, which is thermally attachedthereto. The cooling of the bulb 24 produces a reduction in pressure ofthe gas, which is communicated to the upper side 25 of the diaphragm 2Ithrough the conduit 20, the spring 23 thereafter tending to raise theplunger valve 22 and throttle the ow of refrigerant passing through theoce 34, so that less refrigerant is admitted to the evaporator li. Asthis throttling effect continues, the compressor, which is operating atconstant speed and is assumed to have sufllcient capacity to cool theevaporator, is enabled to reduce the pressure in the evaporator I Iuntil the desired operating pressure is reached, as determined by thesetting of the back pressure valve I2. The constant back pressure valveI2 is provided with an adjusting screw 35 which changes the bias of thespring 3|, and the spring 3l isso adjusted that the back pressure valvebegins to throttle the now of refrigerant through the orifice 32 whenthe desired suc-tion pressure has been reached in the evaporator- II. Asthe unit continues to operate the compressor pulls down to a lowerpressure and temperature in the conduit I4 and in the compressor casingI, but the constant back pressure valve I2 permits only sufcientrefrigerant to be withdrawn' from the evaporator II to maintain thesuction pressure and temperature of the evaporator and suction conduitI3 substantially constant.

So long as the evaporator load remains constant and the unit capacity isunchanged, the system will operate at a condition in which the desiredpressure will be maintained in the evaporator II and will operate at asuction pressure' in the conduit I4 and casing I of the compressor suchthat the unit capacity will be substantially equal to the evaporatorload. Slight variations in the unit capacity due to differences incondensing temperature will only effect the pressure in the conduit I4in the casing I of the compressor without effecting the temperature andpressure of the evaporator II.

Assume now that the load on the evaporator II is increased; refrigerantwhich is being admitted to the' expansion valve II) will be evaporatedbefore it reaches the bulb 24 on the suction conduit I3 and thetemperature of the gas in the y result in a higher operating pressure inthe evap- A orator. However, the increase in the evaporating pressure ofthe refrigerant in the evaporator II acts upon the diaphragm 2li of theconstant pressure valve i2 to open the orice 32 and permit the dow ofmore refrigerant to the compressor 3. Since the constant pressure valvel2 is a throttling device it will adjustitself `to give the properopening and to pass whatever amount of refrigerant is admitted by theexpansion valve II). Thus, the increase in the evaporator load isaccompanied by an increase in the amount ofv refrigerant admited by theexpansion valve Il! but the rise in the pressure which would normallyaccompany this increase in refrigerant and heat load is odset by furtheropening of the back pressure valve i2. The increased evaporator loadeffects an 'increase in the pressure in the suction conduit i4, and theinterior of the casing I to such a point that the unit capacity at thenew pressure in the compressor will give the compressor a capacitysubstantially equal to the evaporator load.

Assuming now that the load on the evaporator is decreased, some of therefrigerant in the evaporator III will not be vaporlzed and will flowinto the suction conduit I3 causing a reduction in the pressure of thegas in the bulb 24. This reduction in pressure is communicated to thechamber 25 above the diaphragm 2l of the expansion valve til so that thespring 23 will force the plunger 22 up to close the orifice 34, thusthrottling the flow of refrigerant through the expansion valve to theevaporator Il. A smaller amount of refrigerant is, therefore, admittedto the evaporator and the normal tendency would be for the compressor 3to lower the pressure of the refrigerant in the evaporator li. However,Vany decrease in the pressure of the refrigerant in the evaporator IIgaeta upon the diaphragm 2@ of the constant pressure valve I2 and theplunger 29 is therefore moved in a direction tending to close theorifice 32, thus decreasing the amount of refrigerant the compressorcasing I will be lowered to such a point that the capacity of thecompressor at the lower suction pressure will equal the evaporator load.l

When the compressor 3 is stopped by operating the manual switch I8 todeenergize the motor 2, the pressure of the refrigerant in theevaporator I I gradually builds up. The increase in pressure during theinactive period tends to open the constant back pressure valve I2, andthe increased Pressure is also communicated to the'. chamber 21 on theunderside of the diaphragm 2| of the expansion valve I0, eventuallyclosing the valve I II, and isolating the evaporator II from the highside of the system. It will be seen, therefore, that, if the motor andcompressor are again started after a shortperiod of time, it will not benecessary to perform as much work to pull the evaporator II down to thedesired suction pressure, as if the pressures in the system hadcompletely equalized.

It will be noted that the thermo-expansion valve I0 is directly effectedby the pressure of the refrigerant in the evaporator II only during thetime that the evaporator is inactive, in order ilrst to eiect a rapidflow of refrigerant to the evaporator as soon as the compressor isstarted, which in turn reduces the temperature of the evaporator to thedesired value very quickly, and secondly to prevent rapid pressureequalization after the compressor is stopped. After the compressor hasbeen started and is in normal operation, the control of the amount ofrefrigerant admitted to the evaporator is dependent upon the temperatureof n the refrigerant vapor leaving the evaporator as translated to theexpansion valve through the medium of the gas in the bulb 24 and theconduit 20.

It will be seen that the capacity of the evaporator may be controlled byadjusting the spring 3| of the constant back pressure valve I2. In thissystem the evaporator capacity will be increased by lowering theevaporator pressure because the lowering of the pressure'will decreasethe temperature of refrigerant in the evaporator and inand haveaccomplished this result in a system where the motor operatescontinuously without being responsive in any way to pressure ortemperature of the system. Our invention, therefore, removes thenecessity for controls to cycle the. apparatus or control the speed ofthe compressor, and maintains a constant predetermined temperature in anevaporator which has small Stor.- age capacity, but is subjected tofluctuating loads. By maintaining the temperature of the evapora- Underthis new condition, the pressure in the conduit Il and y tor and suctionline at a sufficiently high value,

excessive condensation of moisture with resulting dripping thereof onthe material operated upon is prevented.

' While we have shown our invention in but one form, it will be obviousto those skilled in the art that it is not so limited, but issusceptible of various changes and modifications without departing fromthe spirit thereof,A and we desire, therefore, that only suchlimitations shall be placed thereupon as are imposed by the prior art oras are specifically set forth in the appended claims.

What we claim is:

1. In a refrigerating system wherein a refrigerant is compressed,condensed, and evaporated evaporator in which the evaporation ofrefrigerant takes place, means for effecting continuous operation of thesystem and, therefore, continuous evaporation of refrigerant in saidevapora tor, and means for maintaining the temperature of the evaporatorsubstantially constant during continuous operation of the system andregardless of the heat load on said evaporator.

2. In a refrigerating system wherein a refrigerant is compressed,condensed, and evaporated in a continuous cycle, the combination of acompressor for compressing refrigerant vapor, an evaporator in whichevaporation of the refrigerant takes place, means for effectingcontinuous operation of said compressor, flow control means forsupplying varying quantities of refrigerant to said evaporator inresponse to the heat load thereon and valve means for maintaining a.constant pressure in said evaporator during said continuous operation ofthe compressor, regardless of .the heat load on said evaporator.

3. In a refrigerating system wherein a refrigerant is compressed,condensed and evaporated in a continuous cycle, the combination of acompressor for compressing refrigerant vapor, an evaporator in whichvaporization of the refrigerant is effected, a connection for conveyingrefrigerant vapor from the evaporator to the compressor, means forsupplying varying quantities of refrigerant toA said evaporator inresponse to the load thereon,'and a constant pressure valve in theconnection between the evaporator and the compressor for maintaining thepressure and the temperature of the refrigerant in said evaporatorsubstantially constant while continuing constant speed operation of thecompressor and regardless of the heat load on the evaporator.

4. In a refrigerating system in which a refrigerant isfc'ompressed,condensed and evaporated in a continuous cycle, the combination of acompressor for compressing refrigerant, a condenser for liquefying thecompressed refrigerant, an evaporator in which liquefied refrigerant isvaporized, connections for conveying refrigerant from said condenser tosaid evaporator and from said evaporator to said compressor, a valve iny the connection betweenthe condenser and the thereto, and a. constantpressure valve in the connection between the evaporator and thecompressor for maintaining a substantially constant temperature andpressure of the refrigerant in the evaporator while continuing operationof the compressor and regardless of the heat load on the evaporator.

5. The method of operating a refrigerating system embodying anevaporator and a. compressor a substantially constant evaporatortemperature while varying the amount of heat abstracted y therefrom inaccordance with the load.

ROBERT H. TULL. BARTEL J. HOMKEB.

